Radial velocities and binarity of southern SIM grid stars

TL;DR

This study analyzes radial velocities of 1134 southern red giant stars to estimate their binary fraction and RV jitter, aiding the selection of stable astrometric grid stars for space missions.

Contribution

It provides the first large-scale spectroscopic screening of candidate SIM grid stars, estimating their binary rate and RV jitter with limited observations.

Findings

Binary star rate estimated at 32-46%.

RV jitter between 24 and 51 m/s.

Identification of stars with high velocity variations.

Abstract

We present analysis of precision radial velocities (RV) of 1134 mostly red giant stars in the southern sky, selected as candidate astrometric grid objects for the Space Interferometry Mission (SIM). Only a few (typically, 2 or 3) spectroscopic observations per star have been collected, with the main goal of screening binary systems. The estimated rate of spectroscopic binarity in this sample of red giants is 32% at the 0.95 confidence level, and 46% at the 0.75 confidence. The true binarity rate is likely to be higher, because our method is not quite sensitive to very wide binaries and low-mass companions. The estimated lower and upper bounds of stellar RV jitter for the entire sample are 24 and 51 m/s, respectively; the adopted mean value is 37 m/s. A few objects of interest are identified with large variations of radial velocities, implying abnormally high mass ratios.